使用Jersey序列化Java 8流 [英] Serialize Java 8 Stream with Jersey

问题描述

如何使用Jersey序列化Java 8 java.util.Stream< T> 。我试着写一个 MessageBodyWriter ，但我需要知道如何用新的<组合（装饰）现有的 MessageBodyWriters code> MessageBodyWriter 我的流。

How can I serialize a Java 8 java.util.Stream<T> with Jersey. I tried to write a MessageBodyWriter, but I need to know how to compose (decorate) existing MessageBodyWriters with a new MessageBodyWriter for my Stream.

Stream<String> get(){
  return some stream of strings  
}

public <T> class StreamMessageBodyWriter<Stream<T>> 
           implements MessageBodyWriter<Stream<T>> {

  public void writeTo(.......){
    //How can I get the handle to MessageBodyWriter that will write for type T, 
    //so that I can 'collect' the 'java.util.Stream<T>' and write it to 
    //OutputStream
  }
}

推荐答案

但我需要知道如何撰写（装饰）现有的 MessageBodyWriters 我的流

你可以注入 提供商 并使用 getMessagBodyWriter（...） ，将所需的详细信息传递给looku p该类型的特定编写者。例如

You can just inject Providers and use getMessagBodyWriter(...), passing in the required details to lookup the specific writer for that type. For example

@Provider
public class StreamBodyWriter implements MessageBodyWriter<Stream> {

    @Context
    private Providers providers;

    @Override
    public boolean isWriteable(Class<?> type, Type genericType, 
            Annotation[] annotations, MediaType mediaType) {
        return Stream.class.isAssignableFrom(type);
    }

    @Override
    public long getSize(Stream stream, Class<?> type, Type genericType, 
            Annotation[] annotations, MediaType mediaType) { return -1; }

    @Override
    public void writeTo(Stream stream, Class<?> type, Type genericType, 
            Annotation[] annotations, MediaType mediaType, 
            MultivaluedMap<String, Object> httpHeaders, OutputStream entityStream) 
            throws IOException, WebApplicationException {

        Object obj = stream.collect(Collectors.toList());
        Class<?> objType = obj.getClass();

        MessageBodyWriter writer = providers.getMessageBodyWriter(objType, 
                null, annotations, mediaType);

        writer.writeTo(obj, objType, null, annotations, 
                mediaType, httpHeaders, entityStream);

    }
}

如果你看 writeTo ，首先我调用 collect 然后获取返回的类型。然后查找该类型的编写器，然后简单地委托给编写者。

If you look at the writeTo, first I call collect then get the returned type. Then lookup the writer for that type, then simply delegate to the writer.

这是一个测试

@Path("stream")
public class StreamResource {

    @GET
    @Produces(MediaType.APPLICATION_JSON)
    public Response getStream() {
        List<Person> myList = Arrays.asList(
                              new Person("Stack"), 
                              new Person("Overflow"),
                              new Person("Sam"));
        Stream<Person> stream = myList.stream()
                                      .filter(p -> p.name.startsWith("S"));
        return Response.ok(stream).build();
    }

    public static class Person {
        public String name;
        public Person(String name) { this.name = name; }
        public Person() {}
    }
}

C：\> curl -v http：// localhost：8080 / api / stream

结果：

[{name：Stack}，{name：Sam}]

顺便说一句，如果您打算在编写器中操作Stream，可能会考虑使用拦截器。真的不会有所作为，但如果你想坚持单一责任原则，这就是拦截器用于操纵请求体。

As an aside, if you plan on manipulating the Stream in the writer, maybe look into using an Interceptor. Won't make a difference really, but if you want to stick to the Single Responsibility Principle, this is what the Interceptor is for, manipulating the request body.

注意：以上是标准的JAX-RS

Note: the above is standard JAX-RS

特别是对泽西岛，你也可以注入 MessageBodyWorkers ，用于更具体的查找，甚至调用其 writeTo ，如果有人存在，将委托给所需的作家。

Specifically with Jersey, you can also inject MessageBodyWorkers, for more specific lookup, and even calling its writeTo, which will delegate to the required writer, if one exsists.

这篇关于使用Jersey序列化Java 8流的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！